Continuous heating furnace and method of operating the same



Oct. 12, 1948. w. A. MORTON 2,451,349

CONTINUOUS X'HEIA'I'ING FURNACE AND METHOD OF OPERATING THE SAME FiledJan. 12, 194; a Sheets-Sheet 1 N VN Oct. 12, 1948. w. A. MoRToNCONTINUOUS HEATING FURNACE AND METHOD OF OPERATING THE SAME 3Sheets-Sheet 2 Filed Jan. 12, 1943 Oct. 12, 1948. w. A. MORTON 2,

CONTINUOUS HEATING FURNACE AND METHOD OF OPERATING THE SAME Filed Jan.12, 1945 3 Sheets-Sheet 3 Patented, Oct. 12, 1948 CONTINUOUS HEATINGFURNACE AND METHOD OF OPERATING THE SAME William A. Morton, MountLebanon, Pa., assignor, by mesne assignments, to Amsler MortonCorporation, Pittsburgh, Pa., a corporation of Delaware ApplicationJanuary 12, 1943, Serial No. 472,098

15 Claims.

This invention relates generally to heating furnaces and moreparticularly to heating furnaces of the type wherein articles are heatedas they are moved therethrough and the method of operating the same.

This invention is a continuation in part of United States Letters PatentNo. 2,329,211 for Continuous heating furnace and method of operating thesame.

The principal object of this invention is the provision of an improvedcharacter of continuous furnace and the method of operating the same.

Another object is the provision of independent local regulation of thetemperatureof the steel as it travels through the furnace or rests onthe soaking hearth section. This method contemplates the operation ofburners adjacent the discharge end of the furnace chamber to maintainthe steel on the soaking hearth at its proper rolling or workingtemperature during mill delays or shutdowns when little or no heat isrequired of the burners at the charging end.

Another object is the provision for automatically controlling thetemperature of the steel as it is discharged regardless of the rate ofproduction, or rate of firing the heating chamber, or during milldelays.

Another object is the provision of a method for controlling the rate ofheating of the steel in the furnace in proportion with the rate ofproduction without endangering the thermal or physical characteristicsof the stel in the critical heating range.

Another object is the provision of a method for varying the position orlocation of the maximum thermal input within the furnace chamber.

Another object is the provision for introducing the heating medium atboth ends of the furnace chamber and withdrawing all the products ofcombustion from the discharge end of the furnace.

Another object is the provision of a continuous furnace having a solidhearth the under side of which is heated to prevent heat absorption fromthe steel lying thereon, thereby reducing thetemperature differentialbetween the furnace temperature and the waste gases below the hearth.This improvement increases the efllciency of the furnace by lowering thelosses and reducing the fuel consumption.

Another object is the provision of heating the hearth of a continuousfurnace to reduce the temperature gradient from the top to the bottom ofthe steel lying on the hearth.

Another object is the provision of a recuperator 2 the roof of which isemployed as a hearth for a continuous furnace to stop heat loss from thesteel as it is heated when passing along the hearth.

5 Other objects and advantages appear in the following specification andclaims.

A practical embodiment illustrating the principles of this invention isshown wherein:

Fig. 1 is a vertical sectional view of the continuous furnace comprisingthis invention.

Fig. 2 is a cross sectional view taken on the line 22 of Fig. 1.

Fig. 3 is a diagrammatic view illustrating the circuits forautomatically controlling the furnace operation.

Fig. 4 is a graph illustrating the temperature of the furnace and thesteel being heat treated as it passes therethroiigh.

Referring to Figs. 1 and 2 of the drawing, the

furnace illustrated therein comprises the furnace chamber l0 enclosed bythe roof II which has a gradual slope downwardly from the rear orcharging end wall l2 to the front or discharge end wall [3. The roof isarched transversely and is supported exteriorly by thesteel beams Mwhich are assembled in sections forming steps from the front to the rearof the furnace. The side walls It of the furnace extend to thefoundation l8 beneath the furnace. The foundation I6 is irregularbecause substantially half of the length of 40 2 enclose the centermostrecuperator and the outer recuperators are enclosed between theeliterior side walls i5 and the intermediate vertical walls l8.

The roof 20 of the recuperators i'l horizontally divides the furnacechamber Ill into two chambers, the main heating chamber 2| above theroof 20 and the recuperator chamber 22 below the roof 20. Therecuperator chamber 22 is divided longitudinally of the furnace intothree separate 5 passages 23 by the intermediate vertical walls II whichare extended to the front of the furnace where the passageways 23 areconnected to the transverse passage 24 and the vertical outlets 2i. Asolid hearth 26 is laid on the top of the roof I 20. This hearth extendsfrom the charging door of the recuperators l1.

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21 to the gravity discharge slope 28 at the front of 'the "-furnace. Thetop of the division walls formingthe outlets 25 are inclined and carrywater-cooled .skids' which form the rails ofthe gravity discharge slope28 upon which the steel slides asit is being discharged from the hearthi'n the'furnaee chamber. A shortg s'ection 30 ad-'-.

iaccnt-the front end of the hearth 28 serves as the soaking part of the'hearth. I

--That" portion of the rear wall lf above thethe furnace temperature isapproximately 2500' F; the steel on the soaking hearth will beapproximately 200 F. less. This difference may vary slightlybut forpurpose of control the waste gases always bear a direct relation to thesteel temperature whereby the furnace control system may be accuratelyoperated. Y

-'The temperature of the gases discharged fromthe furnace is measured bythe pyrometer 4'Iand hearth I8 is'provided with a rowof large-burnerswhich are supplied with 'preheated air by the duct 32 that extendsaround both sides of the furnace and is'oonnectedto the common aircol-'- supplied with preheated air from the collector 33' through ductssimilar toflthe ducts 32. The control mechanism which automaticallysupplies and regulates fuel fed to the furnace in accordance with thetemperature demands of the furnace together with transfer of the firingfrom the rear burners 3i to the front burners 34 are shown in Figs. 3and 4.

60 represents the blower for delivering air to registered in therecording potentiometer temperature =control -'|8.- This control in turnoperates theservo motor 63- for opening and closing the damper 62 andthereby regulates the amount of.

- air delivered to the furnace for controlling the motor 66.

the recuperator I1 where it is preheated and directed to the burners 3|and'34. A Venturi tube (ii is inserted in the blower inlet whicih iscontrolled by the damper 62 operated by the servo motor 63.

The fuel is supplied through the conduit 64 and I its flow is controlledby the regulating valve 65 which is operated by the motor 66. When thefuel passes from the valve 65 it must flow through an orifice plate 61and then continues through the supply conduit to the burners 3| and 34.Each of these sets of burners is provided with a handoperated valve 68for independently adjusting the flow of fuel to each'of the burners. The

flow of fuel may be read by the meter 69.

The burners are preferably of the induction type and the preheated airin the common ducts while it is induced it is also proportioned by thefuel ratio control. This is important to maintain the proper furnaceatmosphere throughout furnace operations. 7

Fluid pressure lines 10 connect each side of the Venturi throat 6i toone diaphragm of the airfuel regulator II for registering by pressurethey quantity of air flowing to the recuperator. Fluid pressure lines 12also connect each side of the orifice 61 in the fuel line to the otherdiaphragm of the air-fuel regulator and register the quantity of fueldelivered to the furnace. .The quantities of air and fuel are thus keptproportional by means of this ratio regulator control which is operatedby differential pressures created by the flow of air and the quantity offuel is maintained proportional. The quantity of air is previouslydetermined by the temperature of the furnace.

The temperature of the gases being discharged from the furnace throughthe flue 25 has a direct relation to the temperature of the steel on thesoaking hearth 30 which the gases have just passed over, whether thesegases are coming from the main burners 3| during normal operation orfrom the burners 34 during mill delays. When temperature. 1 7

Any change in the quantity of air delivered to the recuperator isregistered as differential pressures in the air-fuel regulator H whichactuates the ratio control 14 for automatically maintaining apredetermined ratio of air .and fuel flowiby operating the fuel valve 65by means of the servo The servo motor 86 may be operated by fluidpressure through the control lines 15. Whenthe properquantity of fuel isdelivered to the furnace for maintaining the predetermined ratio of airand fuel a balance will be created between the diaphragms of theregulator 'H by the pressure differentials registered across the re-.

stricted orifices in the air and fuel lines.

The pressure of the furnace naturally varies with the rate of productionand the rate of firing.

In order to maintain the furnace at a predetermined pressure anatmosphere connection in the furnace is made through the conduit 16 tothe 'pressure regulator 11 for carrying pressure impulses thereto. Theseimpulses are relayed through the furnace pressure control device whichopens a high pressure valve in lines 18 to open ports in the oppositeends of the fluid operator motor 46 for regulating the main damper 45 inthe flue 38 leading to the stack. The furnace pressure regulation issupplemented by a suitable hand control, whereby the pressure to beautomatically maintained may be predetermined and adjusted.

The fluid pressure controls may be supplied with fluid from thereservoir 19, which is connected to a source of fluid pressure.

The control system automatically maintains this continuous type furnaceat a predetermined temperature and under proper pressure and atmosphereconditions. The location of the pyrometer 41 which registers thetemperature of the gases, which bear a direct relationship to the steeltemperature, is important and is'made possi' g bio and practical for thefirst time in continuous furnace practice.

During normal mill operation the potentiometer temperature control 13 ofthe furnace control regulates the flow of air delivered to thefurnaceand the regulator 'H proportions the flow of fuel with thequantity of air being delivered to the furnace. The air and fuel linesare each provided with the Y connections and 81, respectively. forconducting the air and fuel to one of two branch lines. One branch lineconnects with the main burners 3| for normal operation of the furnace.The other branch line connects with the burners 34 for operation duringmill delays.

Each of these branch lines is controlled by a solenoid operated valvewhich preferably has a spring return action for closing the valve. Thisarrangement provides a safety feature in case of a power failure.The-valves 82 and 83, in air and fuel branch lines respectively, controlthe lines leading to the main burners at the rear of the a predeterminedamount the servo motor 63 actuates the selection switch 90 whichdeenergizes the valves 86 and 31, causing them to close and ener thevalves 82 and 83, causing them to open and thereby transfer the firingfrom the front to the rear of the furnace. Thus the furnace has beenrestored to normal operation for continued mill production.

The selection switch 80, which controls the lo -transfer of firing fromnormal operation to mill with electrical energy from any suitable sourcesuch as indicated by the wires 8|.

The switch 90 selectively energizes either set of valves for controllingthe normal operating main burners 3| or the mill delay burners 34. Thisselection is determined automatically by the temperature of the furnace.The furnace controls are adjusted to provide the proper firingconditions for the desired rate of reduction. With this adjustmentnormal operation of the furnace is automatically continued by moving thesteel therethrough at the chosen predetermined rate of speed. If hotsteel is not taken from the furnace at the normal rate, by feeding coldsteel thereto, the furnace temperaturewill quickly rise. l his rise intemperature is immediately registered by the pyrometers 41 in thepotentiometer temdelay operation, may be designed to operate thetransfer valves in the branch lines when 50% of the normal amount of airis delivered to the furnace as stated above. When the transfer is be-.ing made from mill delay operation to normal vantageous in the controlsystem as different fuels and different characters of furnaces mayrequire faster or slower pick up to return them to normal operation.

Again the transfer valves 82, 83, 86 and 81 may be arranged toproportion the quantity of air and fuel between the rear and front ofthe furperature control 13 which energizes the servo I motor 63 toreduce the quantity of air delivered to the furnace. The reduction ofair thus automatically reduces the quantity of fuel through theregulator 1| and the air fuel ratio control 1|. As the quantity of heatenergy delivered to the furnace is reduced, the furnace temperaturefalls to normal.

If no steel is taken from the furnace the temperature'rises very fastand initiates the automatic operation just described. When thepotentiometer control 13 reduces the quantity of air delivered to thefurnace to a predetermined amount, such as 50%, then the servo motor 63throws the switch 90, thereby selectively changing the firing fromnormal operation at the rear of the furnace to the mill delay burners 34at the front of the furnace by deenergizing and closing the air and fuelvalves 82 and 83 and energizing and opening "1e air and fuel valves 86and 81-.

The waste gases from the redirected flames of the mill delay burners 34continue to control the temperature of the steel on the soaking hearth30 and the automatic controls continue to function in the same manner.The fuel consumption during mill delays is naturally materially lessthan that required for normal furnace operation because the small amountof steel on the soaking hearth is all that is maintained at rollingtemperature. Again this steel is not overheated and is always ready foruse.

When mill operations are resumed, hot steel is dis-charged from thecoaking hearth and cold steel is charged into the rear of the furnace,the gases discharged through the flues 25 become cooler because thefurnace temperature drops due toincreased absorption of heat by thecooler steel moved onto the soaking hearth and into the furnace. Thepyrometer 41 then actuates the potentiometer temperature control 13which in turn energizes the servo motor 63 for operating the nace, inwhich case the burners 3| and 34 will all be firing at the same time anda greater differential will be provided between the complete transfer ofthe firing from one end of the furnace to the other.

This automatic control system may be applied to furnaces of this typeother than that disclosed herein. However it is particularlyadvantageous for use with these furnace structures.

If it be necessary to turn off the burners in the main heating chamberbecause the mill is shut down for roll change or repairs, the steel onthe soaking hearth may thus be kept at rolling temperature automaticallyby means of this control system which mechanically transfers the firingoperation from the main burners to the mill delay burners 34, When themill is again ready for hot steel the furnace is prepared to deliver itimmediately from the soaking hearth and the burners in the main furnaceautomatically resume operation in response to initiation of cold steelcharging creating a fuel demand. This represents a material advance inthe continuous furnace art.

The graph illustrated in Fig. 4 shows the temperature conditionsthroughout the continuous furnaces disclosed above. The upper curve F1represents the temperature of the furnace throughout its length when itis being used for low carbon steel. F2 represents the temperature of thefurnace when heating alloy or high carbon steels. The respectivetemperature of the low carbon and high carbon steels as they passthrough the furnace under these conditions is represented by the curvesS1 and S2. Obviously more low carbon steel may be heated under theparticular conditions or safe controlled rates of temperatureacceleration in the same. furnace safely for the first time.

The temperature of an ordinary continuous type of furnace such as thatfound in the prior art is illustrated as curve Fe in Fig. 4. In suchcontinuous type furnaces the temperature within the main heating chamberis highest between the center of the chamber anda soaking chamber',whereas in this improved furnace with above disclosed method of firingthe same, the highest temperature is adjacent the charging end of themain heating chamber and the temperature grad- 7 ually diminishes to thedischarge end of the furnace, thereby providing a preferred state ofthermal equilibrium, in that the gases, steel and furnace parts aresubstantially uniform across the furnace. In ordinary continuous typefurnaces these temperature conditions are not at tained.

Particular attention is directed to the fact that the burners 3!, whichare the only source of heat supply during the normal operation of thefurnace, are located at the rear of the furnace just above the openingthrough which the billets or the like are charged into the heatingchamber 2|, The steel charged into the furnace is either cooled frombeing exposed during previous working steps or is cold because it isbeing initially heated. Thus the newly introduced steel is cold when itis introduced into the main heating chamber 2| and the heating flamesissuing from the burners 3| provide the highest temperature at thecharging end of the furnace. This results in the greatest heatabsorption by the steel as it enters the heating chamber. As the steelmoves to the front of the furnace the rate ofheat ab- ,sorptiongradually decreases because the temperature of the burning gases flowingto the front of the furnace is decreasing and the steel slowly movingconcurrently therewith is increasing in temperature; Thus thetemperature differential'between the gas and the steel becomes lower andthe rate of heat absorption by the-steel becomes correspondingly less.

Under selected firing conditions with the proper thermal load whichdetermines the rate of production of a given furnace, the heat input isdesigned to bring the steel up to the desired temperature when itreaches the soaking hearth and the temperature of the gases passing-overthe steel moving along the soaking hearth is sufiicient to supply thelosses and maintain the steel at the desired temperature. Thus the heatabsorption by the steel is complete before it passes over the soakinghearth and when on the soaking hearth the temperature of the steelbecomes uniform throughout. The products of combus-- tion delivered tothe recuperators are thus higher than the products of combustion beingdischarged from a chamber of a furnace where the highest flametemperature is adjacent the front of the chamber, near or over thesoaking hearth,

and the products of combustion are discharged from the center or therear of the chamber.

A solid hearth furnace is ordinarily employed for heating steel ofirregular lengths and thickness. In some instances the steel may be tooshort to span the water-cooled skids in a continuous furnace wherein thetop and bottom of the steel is heated at the same time. Again long slabsor billets that are only three'and one-half inches or less in thicknesscannot be heated in a continuous furnace having water-cooled skids forcarrying the steel over an exposed lower combustion chamber because theywill sag and become deformed.

The object is to provide a solid hearth continuous furnace in whichsteel of irregular lengths and thickness may be heated as well as heavyslabs and billets of the character that is normally heated from aboveand below when traveling on water-cooled skids. It is impractical toheat thick billets in a continuous furnace having a solid hearth becausethe underside of the hearth is open to the atmosphere and heat iscontinuously absorbed by the hearth from the steel, making thetemperature of the bottom of the billet resting on the hearth materiallylower than that of the top of the billet. The minimum rollingtemperature for soft steel is approximately 2150 F. and the temperatureof a billet ten inches thick in a furnace atmosphere of approximately2450 F. will be 2250 F. at the top and 1900" F. at the bottom, adifferential of 350 F. Continued soaking will not permit the billet tohave a uniform temperature because heat, is being continuously conveyedfrom the billet by the solid hearth. The temperature of the surface ofthe solid hearth is approximately 1800 F, and the underside of thehearth being exposed to the atmosphere is approximately 300 F. Thus thedifferential in temperatureof the hearth is approximately 1500 F. It istherefore impossible to raise the temperature of the underside of thebillet to rolling temperature because these temperature differentialsare excessive and it would require a furnace temperature that would bedestructive to-the upper surface of the steel to have rollingtemperature at the bottom.

By the heating of the underside of the hearth a described above, thetemperature differentials of the steel and the hearth are reducedmaterially, which permits this continuous furnace to be used for heatingheavy slabs and billets, as well'as irregular lengthsand thickness. Forexample, the top of a billet seventeen inches thick moving through afurnace atmosphere of 2450" F. has a temperature of 2250 F. and thebottom has a temperature of approximately 2200 F., producing atemperature difl'erential of 50 F. in the heavy billet. The whole of thebillet is therefore-above the required rolling temperature. The gases atthe soaking hearth 30 are approximately2450 F. and they are alldischarged at the front end of the chamber I0 passing down the outlets25 and through the passageways 23 along the underside of the hearthheating it for the full length thereof. The products of combustion fromthis furnace are discharged at a higher temperature than that of anordinary solid hearth'furnace since there are no heat losses through thehearth from the main heating chamber. The gases n P ssageways 23 and therecuperator chamber 22 are approximately the same as that dischargedfrom the furnace chamber except for a small gradation normally expected.The temperature of the underside of the hearth is approximately 2400 F.and the heat actually flows up through the solid hearth supplying someheat to the bottom of the billet lying in full contact therewith. Thesurface of the solid hearth has a higher temperature than the undersideof the billet because the heat flows from the hearth to the billets. Thetemperature of the hearth is believed to be approximately 2250 F. andthe temperature differential of the hearth, from the underside to thetop, is approximately F. The billets must be kept in contact with thehearth to be heated thereby and to maintain a lower differential throughthe steel.

By heating the solid hearth in this manner the rate of production isincreased one-third and the heat losses of the furnace are materiallyreduced, making the overall eificiency higher. These advantages actuallymake an inoperative furnace structure operative for thick heavy slabsand billets.

I claim:

1. The method of operating a continuous furnace having a continuoussolid hearth over which billets and the like are moved for reheatingwhich comprises the steps of moving the billets on the hearth throughthe furnace chamber from the charging end to the discharge end,introducing heating flames at.the charging end of the furnace chamberand causing all of the gases thereof to move concurrently with thebillets to the discharge end of the furnace chamber, exhausting all ofthe pro-ducts of combustion at the discharge end of the furnace chamber,regulating the flow of the heating planes to produce a gradation oftemperature in the furnace chamber from the charging end to thedischarge end thereof to thermally treat the billets, and heating thehearth to prevent absorption of heat from the billets and to maintain alow temperature gradient between the top and bottom of the billets.

2. The method of claim 1 in which the heating of the hearth isaccomplished by directing the products of combustion to the undersidethereof.

3. In a continuous furnace for heating billets and the like and having acontinuous solid hearth over which the billets are caused to pass fromthe charging end to the discharge end, burners at the charging end ofthe furnace for introducing heating flames which travel in the samedirec tion as the billets for heating the same, a portion of thecontinuous hearth providing a soaking hearth in the furnace over whichthe billets pass before they leave the furnace, and fines at thedischarge end of the furnace for withdrawing all of the products ofcombustion of said flames over the billets on the soaking hearth anddirecting them to the under side of the hearth to heat the same.

4. A continuous furnace for heating billets and the like comprising asolid floor extending substantially the full length of the furnace anddividin the interior thereof into an upper and lower independentchambers, the upper surface of the products of combustion to the lowerchamber.

6. In the structure of claim 4 which also ineludes burners for.introducing heating flames at the charging end of the upper furnacechamber, and means at the discharge end of the furnace for conductingthe products of combustion from the upper chamber to the lower chamber.

7. In the structure of claim 4 which also includes burners forintroducing heating flames into the upper chamber. means at one end ofthe furnace for conducting the products of combustion from the upperchamber to the lower chamber, and fiue means for drawing the products ofcombustion through the lower chamber for substantially the full lengthof the floor and through the heat exchange to discharge.

8. The method of operating a continuous furnece provided with a heatingchamber having a continuous solid hearth extending from the charging endof the chamber to adjacent the discharge end of the same, whichcomprises moving the billets over the hearth, introducing heating gasesat the charging end of the chamber and causing all of said gases totravel concurrently with the billets to the discharge end of the 10 rchamber, and withdrawing all of the heating gases from the chamber atthe discharge end thereof, and regulating the flow of the heating gasesto produce a uniform graduation of temperature in the furnace chamberfrom the charging end to the discharge end thereoft v 9. The method ofclaim 8 which also includes the regulation of the flow of the gases overthe billets to prevent the surface temperature of the billets fromexceeding the bodytemperature thereof when discharged from. the chamber.

10. The method of claim 8 which also includes the control of thetemperature of the heatin gases to regulate the rate of heat absorptionof the billets as they traverse the chamber.

11. The methodof operating a continuous furnace provided with a heatingchamber having a continuous solid hearth extending from the charging endof the chamber to adjacent the dis-- discharged from the heating chamberto-travel beneath the hearth and in contactwith the under surface of thesame toward the charging end of the furnace to prevent the hearth fromabsorbing heat from the billets and thus maintaina low temperaturedifferential between the top and bottom of the billets.

12. In a continuous furnace for heatingbillets and the like, thecombination of a chamber clefined by side and end walls, a roof and acontinu. ous solid hearth extending from the charging end of the chamberto adjacent the dischar e. vfind of the same and alongwhich the billetsare caused to travel from the charging end of the chamber to thedischarge end of the same, means for introducing heating gases at thecharging end of ,the chamber to travel therein toward the discharge endconcurrently with the billets, and means for withdrawing all the heatinggases at the discharge end of the chamber.

13. In a continuous furnace for heating billets and the like, thecombination of a chamber defined by side and end walls, a roof and acontinuous solid hearth extending from the charging end of the chamberto adjacent the discharge end of the same and along which the billetsare caused to travel from the charging end of the chamber to the,discharging end of the same, means for introducing heating gases at thecharging end 'of the chamber to travel therein toward the discharge endconcurrently with the billets, means for withdrawing all the heatingases at the discharge end of the chamber, and means for returning allthe heating gases toward the charging end i of the furnace in contactwith the under surface of the hearth to heat the latter and maintain alow temperature differential between the top and bottom of the billets.

14. In a continuous furnace for heating billets and the like, thecombination of a chamber defined by side and end walls, a roof and acontinuous solid hearth extending from the charging end of the chamberto adjacent the discharge end or the same and along which thebillets arecaused to travel, means for introducing heating gases at the chargingend of the chamber to travel therein concurrently with the billets,means for withdrawing all the heatlng gases at the discharge end of thechamber, a passage beneath the hearth I 11 extending from the dischargeend of the furnace and communicating with the discharge end of thechamber to receive the gases from the latter, a heat-exchanger to whichthe passage conducts said gases, the hearth forming the roof of theheat-exchanger to maintain a low temperature difierential between thetop and bottom of the billets, and means for exhausting the spent gasesfrom the heat-exchanger.

15. The method of operating a continous furnace having a continuoussolid hearth in the furnace for heating billets and the like whichconsists in the steps of moving the billets through thefurnace chamberfrom the charging end to the discharge end, introducing heating flamesat the charging end of the furnace chamber and causing all of the gasesthereof to move concurrently with the billets over the hearth to thedischarge end of the furnace chamber, exhausting all of the products ofcombustion at the discharge end of the furnace chamber, regulating theflow of the heating gases to produce a uniform gradation of thetemperature in the furnace chamber from the charging end to thedischarge and thereof, and directing the discharge products ofcombustion to the underside of the hearth to maintain a low temperaturedifferential and reduce heat absorption from the billets and theREFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 158,862 Nicholson Jan. 19, 1875316,963 Harty May 5, 1885 576,152 Redmond Feb. 2, 1897 1,021,144 GordonMar. 26, 1912 1,797,902 Davis et a1. Mar. 24, 1931 2,133,673 SpencerOct. 18, 1988 2,135,645 Spencer Nov. 8, 1938 2,220,585 Spencer Nov. 5,1940 2,298,149 Morton Oct. 6, 1942 2,329,211

Morton Sept. 14, 1943

